1. Field of the Invention
The present invention relates to an improvement in a susceptor used in a vertical vapor-phase growth system to support and heat substrates which are to be subjected to vapor-phase growth.
2. Description of the Prior Art
As shown in FIG. 1, a reactor used for epitaxial growth includes three elements;
(1) susceptor 1 to hold substrates 7, PA1 (2) reaction chamber, PA1 (3) heating means 3.
Several types of epitaxial reactors having various elements are used--for example, horizontal type, vertical type, barrel type.
In a vertical-type reactor, as shown in FIG. 1, a radio-frequency (RF) induction heater 3 and a susceptor 1 made of electro-conductive material, generally carbon graphite, are used. As shown in FIG. 7, susceptor 1-2 has a number of spot-faced portions 2--2 provided in the surface thereof to receive substrates, respectively, which are to be subjected to vapor-phase growth.
The substrates mounted on each susceptor 1-2 are heated by means of heat transferred and radiated from the susceptor 1-2. The spot-faced portions 2--2 for receiving respective substrates have heretofore been formed so as to have a bottom with a V-shaped cross-sectional configuration (see FIG. 8A), a flat bottom (see FIG. 8B), a bottom constituted by a single curved surface (see FIG. 8C), etc. (for example, see Japanese Patent Application Laid-Open Publication (KOKAI) Nos. 59-50095 and 62-4315).
When a substrate received in a spot-face portion in a susceptor is heated at high temperature, a thermal stress which exceeds the critical strength of the substrate is generated therein and slip, that is, a displacement of crystal planes, occurs. The slip is related to the cross-sectional configuration of the spot-faced portions and, therefore, various considerations have heretofore been given to improve the configuration of the spot-faced portions (for example, see Japanese Patent Application Laid-Open Publication (KOKAI) Nos. 59-50095 and 62-4315). There is also a known method wherein generation of slip is prevented by controlling the radial temperature gradient in each substrate and temperature variations within the plane (for example, see Japanese Patent Application Laid-Open Publication (KOKAI) No. 61-190921).
Thus, the improvements hitherto made in susceptors for vapor-phase growth systems aim mainly at preventing generation of slip in substrates.
Accordingly, in a continuous vapor-phase epitaxial growth reaction, silicon is deposited on the periphery of the reverse side of each substrate and this leads to problems in the device process, for example, damage to the mask during lithography process and peel off of chips during dicing process, which results in a lowering in the product yield.